As has been noted in our previous patents, pipe couplings have been in service since the dawn of the industrial age, and thousands of different designs are known. There is no best coupling for all purposes, so users must choose the features required for a particular application, and then choose the lowest cost coupling meeting those specifications. The variables are many: diameter, diameter variability, degree of sealing required, fluid being transferred, hydraulic pressure, exposure to the outside or not, removable or permanent, weight limitations, space limitations, ease of installation and further factors all of which influence the selection of a coupling.
The present inventors have disclosed and received patents on many design variations, relating to removable band-type couplings for pipes where sealing is required. Many of our designs also provide for resistance to mechanical forces tending to separate one or two unflanged pipes. The present disclosure relates to an improvement in the gripping of the pipes to better resist these axial separation forces.
The present invention is preferably for large diameter pipes, but not limited thereto. Furthermore there are many special designs, for example swage lock systems, which are cost-effective for small copper tubes, the coupling being of moderate weight. A review of the latest US patent applications provides the basis for assessing the state of the art.
In US Patent application 2006/0138776 Ameddure et al. disclose a band-type pipe coupling which is intended to improve sealing in the area of the clamp gap. There is no feature addressing the problem of axial separation except the normal frictional resistance of the seal.
A more sophisticated and complex arrangement is proposed by Lundstrom in US patent application 2006/0192384. A large number of peripheral pressure screws supported in bosses are to be tightened to grip the pipe and to prevent axial movement thereof. For large diameter pipes the proposed design is not competitive in cost relative to a band clamp.
Cuvo et al. disclose a pipe coupling in US patent application 2006/0214422 which is provided with a metal pipe grip washer. The band has a complex shape and is poorly adapted to cope with pipe diameter variations.
Seen in US patent application 2006/0265852 to Snyder, SR. et al. is quite similar to the Cuvo application. It is probably intended only for short small diameter applications as seen by the two grooves which need to be cut in the pipe.
A similar problem is seen in the coupling proposed by Wright in US 2006/0267343. The design relies on a series of axially spaced peripheral teeth. As the pipe may be 250 mm diameter and 6 meters long it is difficult to cut such teeth even in the factory and even more difficult in the field.
The coupling disclosed by Walmsley et al. in US 2007/0085341 has a set of bolts or screw studs on center compression plates which may be removed after axially compressing the coupling. The remaining resistance force to axial separation would be marginal.